1. Field of the Invention
The present invention concerns a spacing profile for a spacing frame, which is to be fitted in the edge area of a double-glazing unit thereby forming an interspace, with a profile body of a material possessing low thermal conductivity and with a metal layer, which is bonded to establish a material fit to the locating walls of the profile body which are intended for contact with the insides of the panes.
Within the scope of the invention, the panes of the double-glazing unit are normally of inorganic or organic glass, without of course the invention being restricted thereto. The panes can be coated or finished in any other way in order to impart special functions to the double-glazing unit, such as for example increased thermal insulation or sound insulation.
The profile body of the spacing profile of material possessing low thermal conductivity constitutes, in respect of volume, the main part of the spacing profile and imparts its cross-sectional profile to it.
By "bonded to establish a material fit" is meant that the profile body and the metal layer are durably bonded to one another, for example by coextrusion of the profile body with the metal layer or by laminating the metal layer on separately, if necessary by means of a bonding agent or similar methods.
For some considerable time it has also been the practice to make use of plastic spacing profiles instead of metal spacing profiles for the manufacture of high thermal-insulation double-glazing units in order to take advantage of the low thermal conduction of the former materials.
By materials with low thermal conductivity in the sense of the invention should be understood those which evidence a coefficient of thermal conductivity which is significantly reduced in comparison with metals, that is to say by at least a factor of 10. The coefficients of thermal conductivity .lambda. for such materials are typically of the order of 5 W/(m*K) and below; preferably, they are less than 1 W/(m*K) and more preferably less than 0.3 W/(m*K). Plastics generally fall within this definition.
Of course, plastics generally possess low impermeability to diffusion in comparison with metals. In the case of plastic spacing profiles, it is necessary therefore to ensure by special means that atmospheric humidity present in the environment does not penetrate into the interspace to the extent that the absorption capacity of the desiccant generally accommodated in the spacing profiles is not soon exhausted, thus impairing the reliability performance of the double-glazing unit. Furthermore, a spacing profile must also prevent filler gases from the interspace, such as for example argon, krypton, xenon, sulphur hexafluoride, escaping from it. Vice versa, nitrogen, oxygen, etc., contained in the ambient air should not enter the interspace. Where impermeability to diffusion is involved below, this means impermeability to vapor diffusion, as well as impermeability to gas diffusion for the gases stated.
2. Description of the Prior Art
To improve impermeability to vapor diffusion, DE 33 02 659 Al, which has been employed for formulation of the preamble of claim 1, suggests providing a plastic spacing profile with a vapor-diffusion impermeable layer (vapor barrier) by applying, or inserting close to the surface, to the plastic profile, on the side facing away from the interspace in installed state, a thin metal foil or a metallized plastic film. This metal foil must span the interspace as completely as possible so that the desired vapor-barrier effect occurs. Such a spacing profile is then bonded by means of a sealant, preferably a polyisobutylene-based butyl sealant, applied thinly to the contact surfaces of the locating walls, to the insides of the panes by exerting pressure. In order to prevent the sealant entering the interspace, the plastic profile body incorporates, at the ends of its locating walls facing towards the interspace, contact ribs projecting in each case significantly past the contact surfaces which come in direct contact with the panes on application of pressure. It has been found detrimental that the sealant coating, as a result of the pressure of adjacent contact ribs, is frequently not sufficiently bonded to the pane surface, so that adhesion of the sealant to the inside of the pane is inadequate.
Another spacing profile is known from DE 298 14 768 U1 of earlier priority date. This high thermally insulating spacing profile comprises a desiccant cavity formed by the plastic profile body, at both sides of which are provided contact flanges for contact with the insides of the panes, which are joined by means of bridge sections to the cavity. On the outside facing away from the interspace in installed state is provided a metal layer which can also extend around the contact flanges as far as their contact surfaces. This embodiment has proved advantageous, as by means of a metal surface, it is frequently possible to achieve better adhesion of the profile to the sealant materials generally used, than is the case with a plastic surface. Here, however, the following problems are observed if one extends the metal layer over the entire locating wall as far as its end facing towards the interspace, it can easily happen during handling, for example when cutting to length or bending the profile, that the free end of the metal layer becomes detached from the locating wall. In addition, it is undesirable for the end of the metal layer to be visible from the interspace. If, on the other hand, one only extends the metal layer over part of the locating wall, it is possible to prevent the metal layer being visible. The separation of the free end of the metal layer described is however also observed in this case. In addition, as a result of this arrangement, a step in the contact surface of the locating wall inevitably occurs at the free end of the metal layer, as a result of which uniform exertion of pressure on a sealant coating applied thinly to the contact surface is rendered difficult or even impossible. Here, the contact surface of the metal layer projecting past the contact surface of the locating wall formed by the profile body by the thickness of the metal layer has an undesirable effect similar to the contact rib in the case of the prior art from DE 33 02 659 Al.